Original paper

Macroinvertebrate 13C variability analysis for the assessment of lake trophic functioning

Borderelle, A.L. Gilmette

Abstract

The aim of this study was to better understand the relationships of within- and among-lake variability of macroinvertebrate carbon stable-isotope ratios with both lake trophic potential and lake trophic functioning. Two approaches based on the macroinvertebrate communities were undertaken on 11 French lakes: the Lake Biotic Index (LBI), a lake biological quality assessment method (Verneaux et al. 2004 a), and the carbon isotopic signatures of macroinvertebrates expressed by metrics of dispersion (standard deviation of the littoral macroinvertebrate mean δ13C values and differences between littoral and deep mean δ13C values (Δδ13C)). The littoral macroinvertebrate mean δ13C values obtained ranged from -11.7 ‰ to -38.6 ‰. This great among-lake variability can be partially explained by different geological substrata on which the lakes are located and, potentially, by the lake organic matter recycling activity. Moreover, the depth-related differences in macroinvertebrate community δ13C (Δδ13C values) or macroinvertebrate taxa (taxon 13C depletion: TΔδ13C) were highly correlated to the values of a LBI sub-index, which was itself correlated to hypolimnion oxygenation and deep sediment organic matter contents. This result suggests that the studied lakes showed various degrees of deep recycled carbon assimilation. The depth-related macroinvertebrate 13C depletion may then be considered as describing the result of lake trophic functioning. However, because no correlation was observed between littoral macroinvertebrate δ13C variability and lake trophic potential, it seemed difficult to conclude as to the influence of different carbon sources on this potential.

Keywords

macroinvertebratesδ13clakestrophic functioning